The present invention relates to a fluid compressor employed in a refrigeration cycle apparatus, having a helical blade type compression mechanism, and designed for compressing a refrigerant gas (i.e., a gas to be compressed).
In recent years, fluid compressors that are referred to as helical blade type compressors are proposed. In this type of compressor, a cylinder is arranged in a sealed case, and a roller serving as a rotating member is eccentrically arranged inside the cylinder. Inside the cylinder, the roller rotates on its own axis or revolves around a given axis.
A blade is interposed between the circumferential surface of the roller and the inner circumferential surface of the cylinders, and a plurality of compression chambers are defined by the blade. A refrigerant gas (i.e., a gas to be compressed in a refrigeration cycle) is sucked into the one-end region of the compression chambers. The refrigerant gas is compressed while gradually moving closer to the other-end region.
Unlike the conventional reciprocating or rotary type compressor, this type of compressor is very reliable in sealing characteristics in spite of its simple structure. In addition, it enables efficient compression and can be easily assembled by use of easily-manufactured parts.
Most of the parts constituting the compression section are formed of iron-based materials. Since the parts of the compression section slide with reference to each other, they are required to have reliable abrasion resistance. Normally, therefore, they are made of cast iron or sintered metal.
The parts jointly define a compression chamber and therefore has a function of sealing the gas. If they are formed of the same iron-based material, they have the same coefficient of thermal expansion, and the clearance between them remains unchanged without reference to changes in temperature. Therefore, the use of the same iron-based material enables the clearance to be as narrow as possible and contributes to improvement of the compression performance.
However, where the clearance between the parts is very narrow, the gas does not easily escape through it, when the pressure in the compression chamber rapidly rises as in the situation where the liquid flows backward. A pressure release mechanism has to be provided to cope with such a situation, but this results in a complex structure.
In this type of compressor, moreover, the relative circumferential speeds between the blade and the roller and between the roller and the bearing are comparatively low. Since these portions of the compressor are easily set in the boundary lubrication condition when the compressor is driven, the roller is mainly formed of an abrasion-resistant material which has a comparatively large specific gravity, just like cast iron. The use of such a material ensures enhanced reliability (improved abrasion resistant characteristics) even under the boundary lubrication condition.
However, the cast iron roller having a large specific gravity has a large inertia weight when the compressor is driven and is disadvantageous in light of the vibration suppression. It is therefore desirable that the roller be as light in weight as possible, so as to suppress both vibration and noise and therefore to improve the performance.
The blade described above is made of a fluoroplastic material, such as tetraethylene fluoride resin (hereinafter referred to as PTFE resin) or perfluoroalkoxy resin (hereinafter referred to as PFA resin), since the use of such a material is advantageous in light of the plasticity, the sealing characteristics, the sliding characteristics, and the environmental resistance (temperature, oil, and refrigerant).
In order to improve the abrasion resistance, a composite material is normally used for forming the blade. That is, inorganic fibers (e.g., glass fibers and carbon fibers), a solid lubricant and an organic filler are contained in the material of the blade.
Since a fluoroplastic material greatly varies in size when it thermally expands, clearances a and b defined between the blade D and the wall of the helical groove H, which is formed in the piston P arranged inside the cylinder C, are set to be minimum values when the temperature is highest (during operation of the compressor), in consideration of the compression efficiency and the size variation of the blade D due to the thermal expansion.
However, if the clearances are set or determined in this manner, they may be too large when a compression operation has just been started or in the other low-temperature situations. If this occurs, the sealing characteristics between the components are degraded, and an intended compression performance may not be attained.
It should be noted that the fluoroplastic blade D is soft and may easily bend due to the differential pressure. As shown in FIG. 14, moreover, the blade D may be rubbed at one side with the edge portion Z of the helical blade H. It should be also noted that the elastic modulus may decrease due to the thermal expansion, and the blade may be permanently deformed under an extremely high state of pressure.
The first object of the present invention is to provide a fluid compressor which enables pressure release to be easily done if the liquid flows back in the compressor or under a low-pressure condition as in the initial stage of operation, and which therefore enhances the compression performance under a high-temperature condition during operation.
The second object of the present invention is to provide a fluid compressor wherein the roller (a rotating member) is formed of a pre-selected material such that it is light in weight and highly improved in abrasion resistance and such that the vibration and noise are suppressed, and which is improved in compression performance.
The third object of the present invention is to provide a fluid compressor which suppresses the effects the thermal expansion and the pressure conditions may have on the helical blade by using a pre-selected material for forming the helical blade, and which is improved in compression performance.
The first object of the invention is realized by providing a fluid compressor that includes a helical blade type compression mechanism made up of a cylinder, a rotating member arranged inside the cylinder, and a helical blade interposed between the rotating member and the cylinder. The feature of the fluid compressor is that the cylinder, the rotating member and the cylinder are formed of materials such that their coefficients of thermal expansion satisfy the relationships: Blade greater than Rotating Member greater than Cylinder.
The second object of the invention is realized by providing a fluid compressor that includes a cylinder, a rotating member arranged inside the cylinder, and a helical blade interposed between the rotating member and the cylinder, the rotating member being formed of an aluminum alloy material.
The third object of the invention is realized by providing a fluid compressor that includes a cylinder, a rotating member arranged inside the cylinder, and a helical blade interposed between the rotating member and the cylinder. The blade is formed of a material selected from the group of a PEEK (polyether ether ketone) resin material, a PES (polyether sulfone) resin material, a PEI (polyether imide) resin material, a PAI (polyamide imide) resin material, a TPI (thermoplastic polyimide) resin material, an LCP (liquid crystal polymer such as every kind of aramotica polyester) resin material, and a PPS (polyphenylene sulfide) resin material.
According to the first invention, pressure release can be easily performed in the case where the liquid flows back or under a low-temperature condition as at the time of actuation. In addition, the compression performance can be improved under a high-temperature condition during operation.
According to the second invention, the roller (i.e., a rotating member) is formed of a pre-selected material, so that it is light in weight and highly improved in abrasion resistance. The vibration and noise are therefore reduced, and the compression performance is improved.
The third object of the present invention is to provide a fluid compressor which suppresses the effects the thermal expansion and the pressure conditions may have on the helical blade by using a pre-selected material for forming the helical blade, and which is improved in compression performance.